Actuating device for an on/off valve

Abstract

An actuating device for an on / off valve having a pneumatic drive that is connected to a compressed air supply by a solenoid valve, wherein when driven with a control voltage, the solenoid valve ventilates the pneumatic drive with the compressed air and, when the control voltage is not present, vents the pneumatic drive. The pneumatic drive moves the on / off valve into an operating position during ventilation and moves it into a safety position during venting. To permit the performance of partial-stroke tests in the simplest way possible, a device for performing the partial-stroke test includes a controllable switch which is closed in a quiescent state, and in this case supplies the control voltage to the solenoid valve. The controllable switch is opened by a control signal that is generated to perform the partial-stroke test. The control signal is supplied to the controllable switch by a position switch that is closed in the operating position of the on / off valve and is opened when the on / off valve reaches a predefined position in the direction of the safety position.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This is a U.S. national stage of International Application No. PCT / EP2008 / 059255, filed on 15 Jul. 2008. Priority is claimed on German Application No. 10 2007 034 059.3, filed on 20 Jul. 2007.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to an actuating device for an on / off valve having a pneumatic drive which is connected to a compressed air supply by a solenoid valve, wherein the solenoid valve ventilates the pneumatic drive with the compressed air when driven with a control voltage and vents the pneumatic drive when the control voltage is not present, and the pneumatic drive moves the valve into an operating position during ventilation and moves the valve into a safety position during venting, and a means for performing a partial stroke test.[0004]2. Description of the Related Art[0005]In a known actuating device disclosed in DE 10 2006 003 750 A1 or DE 10 2005 004 477 A1, a pneumatic on / off valv...

AI Technical Summary

Benefits of technology

[0008]It is therefore an object of the invention to provide a way to perform partial stroke tests on pneumatically driven on / off valves using means which are as simple as possible.

[0010]In response to the control signal which is generated, for example, by a control system, the controllable switch interrupts the voltage supply for the solenoid valve. As a result, the solenoid valve is deactivated and the pneumatic drive is consequently vented. The valve then moves from the operating position to the predefined position, where the position switch opens and interrupts the path of the control signal to the controllable switch when the predefined position is reached. Therefore, the controllable switch again shuts down the voltage supply for the solenoid valve which, activated thereby, restores the pneumatic connection between the position regulator and the compressed air supply. As a result the movement of the valve is stopped and reversed. The predefined position at which the position switch opens is selected such that ongoing operation of the installation in which the valve is installed is disrupted only to an insignificant extent by the valve movement during the test. In addition to the very simple and cost-effective implementation of the means for performing the partial stroke test, another advantage of the actuating device in accordance with the invention is that the partial stroke test is used not only to test the function of the fitting comprising the valve and pneumatic drive but also to test the solenoid valve.

[0013]Another advantage of the actuating device the invention is that the test can be performed independently of the respective computation cycle time of the control system, on the one hand, and independently of the reaction speed of the actuator, on the other hand. The duration of the control signal generated by the control system is not critical because the movement of the valve is stopped and reversed anyway when it reaches the predefined position. Here, the control signal is preferably generated for such a long time that the valve repeatedly oscillates about the predefined position. This occurs because the valve is moved back again after the predefined position has been reached, with the result that the position switch closes again; the control signal which is present is then switched through to the controllable switch again, with the result that the latter opens, the solenoid valve is deactivated and the valve is moved to the predefined position again. This operation is repeated as long as the control signal is generated, with the result that the valve oscillates about the predefined position. The respective computation cycle time of the control system is not critical for the evaluation of the test, i.e., the abovementioned evaluation of the current resulting from the control signal or the evaluation of the control signal routed to the signaling output, because the control signal must be generated only for a sufficient length of time.

Problems solved by technology

The predefined position at which the position switch opens is selected such that ongoing operation of the installation in which the valve is installed is disrupted only to an insignificant extent by the valve movement during the test.

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